Wide as fuck looks quality, but too big looks daft to me.

17s on a Sierra (but ideally 9/10 inch wide)
18s on an EscCos (width as above)

Bigger WOULD look better, if it was physicly possible to get the car back down to a normal ground clearance (as its not the arch gap, its the ground clearance that makes it look stupid), but that generally would need some SERIOUS slamming, which would need lots of work.

It CAN be done to look right tho, check this out...